High energy density batteries are typically needed and used in oil drilling operations, namely to power various downhole electrical equipment, and are frequently of the lithium metal anode type, which provide the needed high energy density in comparison to conventional primary batteries (ie non-rechargeable type batteries).
Typically, in oil drilling operations such batteries are located downhole, proximate a drill bit, to provide electrical power to downhole equipment, including sensors and measurement-while-drilling (“MWD”) mud pulsers, which send mud pulses encoded with information from such sensors uphole to surface so as to assist drilling operators in steering the drilling equipment into oil bearing formations, and further giving data as to the types and densities of rock formations encountered during the drilling of such oil wells.
As well depth increases, temperatures may increase from an ambient surface temperature (of say, 23° C.) to temperatures exceeding 100° C., and frequently temperatures in the range of 125° C. to 200° C. are typically encountered at several thousand meters of well depth.
Lithium batteries typically employ lithium metal or a lithium alloy as the anode. Substantially pure lithium may be used as the anode, and in certain types of lithium batteries liquid thionyl chloride [SOCl2] may be used as the cathode, to produce a flow of electrons. The electrochemical oxidation-reduction reaction which occurs to produce such flow of electrons may be as follows:at the anode: Li→Li++e−at the cathode : 4Li++4e−+2SOCl2→4LiCl+SO2+Soverall reaction: 4Li+2SOCl2→4LiCl+SO2+S
Unfortunately, pure lithium metal has a melting temperature of 180.5° C., and standard lithium batteries are accordingly limited to temperatures of about 160° C. to thereby avoid melting of the lithium anode within the battery and consequent explosion of the battery, or at a minimum failure of the operation of the battery. Accordingly, lithium batteries which employ substantially 100% lithium as the anode will typically fail at high temperatures of the magnitude encountered when drilling several thousand meters beneath the surface, where temperatures are often, as mentioned above, in the 200° C. range.
It is known to alloy lithium metal in a lithium battery with 10% magnesium in order to raise the melting point of the resulting 90% Li-10% Mg alloy, thereby raising the maximum temperature to which such a lithium battery may be exposed to up to 200° C., thus rendering lithium-mg alloy batteries usable in downhole applications where temperatures may regularly approach such temperature. (Battery manufactures typically stipulate such batteries are temperature- limited to 180° C., to thereby provide a small “safety buffer”.)
It is further known to alloy lithium metal in a lithium battery with 25% magnesium in order to raise the melting point of the resulting Li—Mg alloy anode up to 220° C., thereby raising the maximum temperature to which such a lithium battery may be exposed, thus rendering lithium-mg alloy batteries usable in downhole applications where temperatures may regularly approach such temperature. (Battery manufactures typically presently stipulate such batteries are temperature limited to 200° C. to thereby similarly stipulate a small “safety buffer” of approximately 20° C.).
Notably, however, while alloying the lithium in the lithium anode with magnesium of up to 25% allows operation of such battery up to the relative high temperature of 200° C., unfortunately such step has the negative side effect of significantly reducing the power and voltage available from such battery at lower temperatures, namely temperatures less than about 50-100°, particularly where a battery may have been sitting idle at such room temperature for periods of approximately forty (40) days or more. This negative side effect produces a significant obstacle to downhole tool companies desiring to test electronic equipment (which is to be powered by such batteries at surface under ambient temperatures, typically at temperatures less than 50° C. and typically at ambient room temperature of approximately 23° C.) to ensure such equipment is properly operating at surface before inserting such equipment downhole for use in drilling operations. This is due to the fact that the power and voltage available from such a lithium metal alloy anode battery at ambient temperatures, for example 23° C., is relatively low, and not sufficient to allow adequate and proper testing of the electrical equipment in the tools powered by such battery at well surface due to insufficient power/voltage supplied by such battery at such ambient temperatures.
To overcome the above negative side effect, downhole tool companies presently apply a heater blanket to tools containing a lithium battery (or battery pack) at surface, in order to significantly raise the temperature of the battery(ies) within the tool at surface to a range of about 50-70° C., in order to thereby obtain sufficient power and voltage from such lithium battery(ies) at such higher temperatures to allow equipment to be tested at surface to ensure proper operation before being inserted downhole.
Unfortunately, malfunction of the heater and/or overheating of the lithium battery(ies) will result (and has resulted) in explosion of such lithium battery(ies) on a number of occasions. This is a serious and substantial safety concern at a drill site, where risk to worker safety and risk of damage or loss of expensive sensor equipment, are serious and over-riding concerns. Unfortunately, overheating of such lithium-mg alloy batteries has resulted in at least one worker fatality due to the resulting explosion of the lithium battery during heating.
Accordingly, a real and substantial need exists in the downhole tool industry for a battery which can provide sufficient power and voltages [typically 3.6 to 3.9 volts (open circuit) from a single cell ] to various electrical equipment at relatively low ambient temperatures such as in the range of 23° C. for a brief initial period to allow testing of such equipment at surface, but which battery may be subsequently exposed to higher temperatures in the range of up to 200° C. and will continue to reliably operate when such battery and associated downhole tool is located downhole.